1. Field of the Invention
This invention relates to a manufacturing method of piezoelectric film element, a piezoelectric film element and a piezoelectric device.
2. Description of the Related Art
A piezoelectric material is processed so as to form various piezoelectric elements in accordance with a variety of the intended uses, in particular, is widely used as a functional electronic component such as an actuator that allows an object to be changed in shape when an electric voltage is applied thereto, a sensor that generates an electric voltage due to the change in shape of the element.
As the piezoelectric material that is used for the application of the actuator and the sensor, a lead-based ceramics that has a large piezoelectric property, in particular, a Pb(Zr1-XTiX)O3 based perovskite type ferroelectric that is referred to as a PZT has been widely used. The PZT ceramics is formed by sintering oxide materials.
On the other hand, at present, various electronic components become more downsized and upgraded, thus it is strongly needed for the piezoelectric element to be downsized and upgraded. However, a piezoelectric material manufactured by a conventional manufacturing method such as a sintering method, particularly if it has a thickness of not more than 10 μm, is configured to have a thickness that is close to the size of the crystal grain constituting the material, thus the influence thereof cannot be ignored. Consequently, a problem is caused that variation and deterioration in the property become prominent. For the purpose of preventing the problem, a forming method of a piezoelectric material in which a thin film technology and the like are applied instead of the sintering method has been investigated.
Recently, a PZT thin film formed by a RF sputtering method is put into practical use as a printer head of a high-definition and high-speed ink-jet printer and a downsized and low-cost angular rate sensor (for example, refer to JP-A-H10-286953). In addition, a piezoelectric film element that uses a lead-free piezoelectric film of potassium niobate is also proposed (for example, refer to JP-A-2007-19302).
When an actuator or a sensor is manufactured by using a piezoelectric film, it is needed for the piezoelectric film to be processed by a microfabrication process so as to have a beam shape or a turning fork shape. However, a lead-free alkali niobate based compound (hereinafter referred to as “KNN” for short) having a perovskite structure that is a lead-free piezoelectric material has a problem that it is a processing resistant material, in addition to this, when the KNN film is etched by using a fluorine (F) system gas, a residue such as KF, NaF remains, so as to reduce a production yield in later processes (e.g., refer to Fumimasa Horikiri et al. “Etching Characteristics of (K, Na)NbO3 piezoelectric films by Ar—CHF3 plasma” the 71st Annual Conference of Japan Society of Applied Physics, Lecture Proceedings, 16p-NJ-10 (2010)).
In the microfabrication of the piezoelectric film, if the process is required to be carried out with a high degree of accuracy, it is necessary not only that the piezoelectric film can be processed in a short time, but also that the process can be selectively stopped at a lower electrode layer. In addition, it is necessary to have the piezoelectric film oriented to obtain a high piezoelectric property. Thus it is necessary to use a lower electrode layer of Pt or the like.
As described in Fumimasa Horikiri et al. “Etching Characteristics of (K, Na)NbO3 piezoelectric films by Ar—CHF3 plasma”, by the inventors et al. of the present application, a manufacturing method is proposed that is capable of processing the KNN film by a dry etching technology using a mixture gas of Ar gas and a reactive gas such as CHF3 gas, and is capable of obtaining a high etching selectivity at the lower electrode layer comprised of Pt, so as to realize the microfabrication of the KNN film.